Hydrocarbon tracers for use in the conversion of hydrocarbons



United States Patent 3,247,097 HYDROCARBON TRACERS FOR USE IN THE CONVERSION OF HYDRGCARBONS Anneile E. van Rosenberg, Baytown, Tern, and Robert L. Huli, Elizabeth, N .J., assigmors, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N J a corporation of Delaware No Drawing. Filed Dec. 13, 1961, Ser. No. 159,166 5 Claims. (Cl. 208-113) The present invention is directed to radioactive hydrocarbon tracers. More particularly, the invention deals with metallic porphyrin chelates synthesized with metallic radioactive isotopes. In its more specific aspects, the present invention is directed to the use of these radioactive metallic porphyrin chelates as radioactive hydrocarbon tracers.

The use of radioactive tracers in industry, medicine and agriculture is well known. In many instances radioactive tracers have led to important discoveries as well as improving and developing known techniques. However, in any operation employing tracer materials the success of the operation is dependent on the choice of tracer material used. Many factors must be considered in choosing a radioactive isotope; the availability and cost of the radioisotope, and the nature of the problem to be studied are merely a few. Accordingly, there is a continuous search for new and improved radioactive tracers which are adaptable for a variety of radioactive tracing operations.

The present invention may be briefly described as radioactive metallic porphyrin chelates which are effective hydrocarbon tracers. The tracers may be synthesized from porphyrin-type compounds and the radioactive iso topes of metals to form a radioactive metal porphyrin. The metallic porphyrin chelates of the present invention are desirable hydrocarbon tracers since they are oil soluble and their composition may be varied to produce compounds having boiling points in the range of about 100 to about 800 C. In addition, the chelates of the present invention are relatively stable and many are known to be volatile under vacuum distillation conditions, and hence, are valuable radioactive hydrocarbon tracers in petroleum processes.

In the radiochemical tracing of hydrocarbons through operating units, the use of external, continuous detection equipment is more efficient than the collection of samples for subsequent analysis and more feasible than the protection of internal detection systems from high temperatures and pressures which otherwise would be necessary. Neither carbon nor hydrogen have radioisotopes which emit gamma radiation, the type of radiation capable of penetrating the usual thicknesses Otf iron and/or concrete vessel walls. Accordingly, the hydrocarbon tracers of the present invention are preferably made by incorporation of an inorganic, gamma emitting isotope in a porphyrin-type molecule.

The metallic porphyrin chelates of the present invention have been found useful in tracing hydrocarbons in petroleum operations, especially those carried out at high temperatures and pressures. Due to the great stability and high boiling points of many of the radioactive metallic porphyrin chelates, these compounds are suitable tor tracing the feed stocks and especially the higher boiling portion of the feed in a transfer line conversion reactor such as a cracking reaction zone wherein the boiling range of the feed to the catalytic cracking zone is approximately 260 to 650 C. The hydrocarbon tracers of the present invention are further advantageous in determining rates of flow, residence or contact time of a hydrocarbon in a specific vessel, or the mixing pattern 3,247,097 Patented Apr. 19, 1966 of a hydrocarbon in various petroleum operations. The volatility and high boiling points of the porphyrin chelates enhance their use in determining efficiency of tractionating column or determining entrainment of materials wherein the materials studied have about the same high boiling points as the radioactive metallic porphyrin chelate used in the tracing operation.

The radioactive metallic porphyrin chelates of the pres ent invention are preferably synthesized by selecting a solvent or solvents wherein the metallic radioisotope and the porphyrin chelate are heated in a single phase. The porphyrin-type compounds are usually soluble to some degree in most organic solvents. However, the selection of the solvent is usually determined by the metal radioisotope or the radioactive metal salt since they are more difficult to put into solution since they are soluble in only some inorganic and organic acids and bases. When more than one solvent is required, the solvents are selected such that the solvents are miscible one with another. Three general methods of synthesizing the radioactive metallic porphyrin chelates may be used. The general methods include the use of an acid medium, a weakly alkaline medium, and a strongly alkaline medium. In employing the acid medium, glacial acetic or formic acid is used to dissolve the radioactive metal or metal salt and porphyrin into a single phase solution. However, due to the slight solubility of porphyrins in glacial acetic acid alone, a variant may be employed wherein a chloroform solution of the porphyrin is added to the solution of radioactive metal or metal salt in glacial acetic acid. The synthesis may also be accomplished by adding the radioactive metal or metal salt to a hot solution of the porphyrin in pyridine. The use of the Weakly alkaline medium is a variant of the strongly alkaline method wherein the radioactive metal or metal salt is dissolved in a strong base such as alcoholic potassium hydroxide and added to a porphyrin solution in pyridine.

The porphyrin-type compounds which are used in the present invention are characterized by the porphyrin ring structure which is a heterocyclic structure consisting of four pyrole rings united by methylene groups. The preferred porphyrin compound in the practice of the present invention is the a, B,'y,E-tetraphenylporphyrin. Other porphyrins are the phthalocyanines and the naturally occurring porphyrins such as those listed on page 360 of Chemistry of the Metal Chelate Compounds by A. E. Martell and M. Calvin (Prentice-Hall, Inc., 1952), which disclosure is incorporated herein by reference.

' The selection of the metallic radioisotopes used in the synthesis of the porphyrin chelates of the present invention depends principally on the boiling point, molecular weight, reactivity or stability required of the radioactive 'metallic porphyrin by the nature of the tracing operation. Practical limitations are set by the cost, availability and half-life of the metallic radioisotope. Since safety is a primary factor in using radioactive tracers, the half-life of the radiosotopes used must be sufiiciently long to accomplish the beneficial results of tracers but be of relatively short-life to avoid any long term contamination of the units wherein the tracer is used. If the tracing operation is carried out experimentally in vessels which may be thoroughly cleaned, the half-life of the isotope becomes of less importance. The choice of metallic radioisotope, therefore, varies according to the tracing operation to be performed. Suitable radioactive isotopes are the radioisotopes of the metals within the solid lines of the table Periodic Classification of Chelate-Forming Metals on page 182 of Chemistry of the Metal Chelate Compounds by A. E. Martell and M. Calvin. Radioactive isotopes and their half-lives which are exemplary of the present invention are manganese-52 days), zinc-65 (245 days), iron-59 chloride (45.1 days), nickel-65 (2.5 hours), cadmium-115m (43 days), cadmium-115 (53 hours), cadmium-109 (1.3 years), nickel-63 (125 years), thallium- 204 (4.1 years) and tin-113 (115 days). The preferred radioisotope is gold-198 having a half-life of 2.7 days.

The invention will be further illustrated by the following specific examples which are given by way of illustration and not as limitations on the scope of the invention. The synthesis of gold-198 chloride tetraphenylporphyrin was carried out as follows:

Gold-198 chloride is received from Oak Ridge only in a 1 N solution of hydrochloric and nitric acids. Twenty to thirty milligrams of gold-198 chloride (this amount as shipped from Oak Ridge contains about 500 millicuries of gold-198) in the aforementioned hydrochloric-nitric acid solution plus 15 milliliters of glacial acetic acid are placed in the reaction flask. The entire solution is reduced to dryness by distillation and vacuum. The acetic acid is added in order that the hydrochloric and nitric acids may be completely removed. If a little acetic acid is left, no deleterious effects on the subsequent synthesis is experienced since acetic acid is one of the solvents in the reaction. Twenty to thirty milligrams of a,[3,'y,5- tetraphenylporphyrin in 50 milliliters of chloroform and one gram of anhydrous sodium acetate in 50 milliliters of glacial acetic acid are then added to the reaction flask. The reaction mixture is distilled until only about one-half of the acetic acid remains. The mixture is then cooled and filtered. The radioactive gold-198 chloride tetraphenylporphyrin appears on the filter as blue-red crystals. The gold-198 chloride tetraphenylporphyrin was used in a study of catalytic cracking transfer line performance. Specifically, the radioactive hydrocarbon tracer was used for determining the flow pattern of high boiling compounds in the feed injection zone. The gold-198 tetraphenylporphyrin crystals were dissolved in a mixture of pyridine and benzene. This radioactive solution was then added to some filtered gas oil feed to the catalytic cracking transfer line to form a master batch. After final dilutions with gas oil, each charge when prepared, consisted of approximately 25-50 millicuries of gold-198 in 50 milliliters of the hydrocarbon blend. Charges were injected intermittently into the transfer line reactor. The progress of the gold-198 was followed by scintillation crystals attached to count rate meters which fed signals to a high-speed multichannel recorder. The scintillation crystals were used as preferred detectors. A detector was located at the point of injection to establish the time the labeled feed pulse entered the unit, and other detectors were placed above and below the injection point for ob servation of the pulse flow pattern. The isotope was found to be traveling at velocities above the feed inlets greater than about feet per second, the individual rates being dependent upon the injection position and the section of the transfer lines being monitored. In general the velocities observed were higher than those formerly observed for the catalyst. Since the gold-198 would deposit on the catalyst if the compound cracked, and the high velocity indicated the gold-198 was not on the catalyst, it could be assumed that the compound acted as a heavy feed molecule and provided data on the feed velocity above the injection point. Catalyst particles are known to have high residence times at the upper detection levels. Since the gold-198 also had long residence times at these levels, the compound apparently cracked near these detection points, and the gold-198 deposited on the catalyst. The information obtained on heavy feed pattern and velocity is presently being employed to improve transfer line reactor design. This successful demonstration of the utility of the radioactive metallic porphyrin chelate has proved that a new class of hydrocarbon tracers are now available to radiochemists.

The nature and objects of the present invention having been completely described and the best mode thereof set forth, what we wish to claim as new and useful and secure by Letters Patent is:

1. A method for preparing radioactive gold-198 chloride tetraphenylporphyrin comprising evaporating to dryness in a reaction flask the metallic gold-198 chloride in a solution comprising glacial acetic acid, adding to said flask tetraphenylporphyrin and sodium acetate in a solution of chloroform and glacial acetic acid to form a reaction mixture, distilling said reaction mixture until only a portion of said glacial acetic acid remains, cooling said reaction mixture, filtering the resulting gold-198 chloride tetraphenylporphyrin and recovering same as a bluish-red solid.

2. In the method of tracing hydrocarbons through a petroleum processing unit, the improvement which comprises injecting a radioactive metallic porphyrin chelate which is soluble in hydrocarbon oil into said unit, and detecting said radioactive chelate at points where the flow pattern of the hydrocarbon may be observed.

3. A method in accordance with claim 2 wherein the porphyrin chelate is the gold-198 chloride of te-traphenylporphyrin.

4. A method in accordance with claim 2 wherein said operating unit is a catalytic cracking transfer line reaction zone and the detecting is carried out at the injection point and other points along the hydrocarbon flow path.

5. A method in accordance with claim 4 wherein said radioactive metallic porphyrin chelate is the gold-198 chloride of tetraphenylporphyrin.

References Cited by the Examiner UNITED STATES PATENTS 3/1960 Weil et al. 260-4291 10/1960 Beebower et al. 252--455 ALPHONSO D. SULLIVAN, Examiner. 

2. IN THE METHOD OF TRACING HYDROCARBONS THROUGH A PETROLEUM PROCESSING UNIT, THE IMPROVEMENT WHICH COMPRISES INJECTING A RADIOACTIVE METALLIC PORPHYRIN CHELATE WHICH IS SOLUBLE IN HYDROCARBON OIL INTO SAID UNIT, AND DETECTING SAID RADIOACTIVE CHELATE AT POINTS WHERE THE FLOW PATTERN OF THE HYDROCARBON MAY BE OBSERVED.
 4. A METHOD IN ACCORDANCE WITH CLAIM 2 WHEREIN SAID OPERATING UNIT IS A CATALYTIC CRACKING TRANSFER LINE REACTION ZONE AND THE DETECTING IS CARRIED OUT AT THE INJECTION POINT AND OTHER POINTS ALONG THE HYDROCARBON FLOW PATH. 